Synthesis, Structure, Bonding, and Reactivity of Metal Complexes Comprising Diborane(4) and Diborene(2): [{Cp*Mo(CO) 2 } 2 {μ‐η 2 :η 2 ‐B 2 H 4 }] and [{Cp*M(CO) 2 } 2 B 2 H 2 M(CO) 4 ], M=Mo,W

The reaction of [(Cp*Mo) 2 (μ‐Cl) 2 B 2 H 6 ] ( 1 ) with CO at room temperature led to the formation of the highly fluxional species [{Cp*Mo(CO) 2 } 2 {μ‐η 2 :η 2 ‐B 2 H 4 }] ( 2 ). Compound 2, to the best of our knowledge, is the first example of a bimetallic diborane(4) conforming to a singly bridged C s structure. Theoretical studies show that 2 mimics the Cotton dimolybdenum–alkyne complex [{CpMo(CO) 2 } 2 C 2 H 2 ]. In an attempt to replace two hydrogen atoms of diborane(4) in 2 with a 2e [W(CO) 4 ] fragment, [{Cp*Mo(CO) 2 } 2 B 2 H 2 W(CO) 4 ] ( 3 ) was isolated upon treatment with [W(CO) 5 ⋅thf]. Compound 3 shows the intriguing presence of [B 2 H 2 ] with a short B−B length of 1.624(4) Å. We isolated the tungsten analogues of 3 , [{Cp*W(CO) 2 } 2 B 2 H 2 W(CO) 4 ] ( 4 ) and [{Cp*W(CO) 2 } 2 B 2 H 2 Mo(CO) 4 ] ( 5 ), which provided direct proof of the existence of the tungsten analogue of 2 .